Unamplified DNA enriched for the DMPK gene through the CRISPR-Cas9 approach was sequenced by LRS in four patients with myotonic dystrophy type 1 (DM1), revealing more interruptions than those detected by RP-PCR and providing sensitive expanded allele-specific characterization of methylation levels, proposed as more reliable markers of the severe congenital form compared to repeat length. This evidence concerns the gene DMPK and myotonic dystrophy type 1.